A new index of aggregation for animal counts.

A new index is described that is especially appropriate for measuring the aggregation of entomological data in the form of counts per sample unit and that can make use of spatial information when it is available. Calculation of the index is based on a comparison of the effort required of individuals in a sample to achieve complete crowding with that to achieve complete randomness. The power of tests of randomness based on this index is found to be greater than those based on the index of dispersion, especially when spatial information is available.